How to model a tinfoil hat? (aluminium foil texture as a mesh)
You may achieve it randomizing the mesh a bit using simple modeling tools, but it demands some experimenting to make it look good.


Model the hat starting from a cube subdivided with a subsurf modifier (4-5 subdivisions). Apply the modifier. Subdivide the hat (with W-->Subdivide) to create a dense geometry. With the all vertices selected press Ctrl+T to trangulate faces. Unselect everything with A, go to Select-->Random (set it's value to about 30-50%), then press Ctrl+E-->Rotate Edge CW. It'll give a bit randomness to the mesh's vertices positions.


Grab selected vertices upwards (G,Z), then scale them outwards a bit (S). Crease the selected vertices with Shift+E. Add a subsurf modifier and smooth the mesh (T-->Edit-->Shading-->Smooth).


Finally to randomize the look of the hat even more, select some vertices and press Ctrl+V-->Smooth Vertex.